This invention generally relates to an electronic sound signal generator which is suitable for use in electronic musical instruments or other tone generating devices, sound signal processing devices or the like, and more particularly to such an electronic sound signal generator which is capable of achieving a scratch sound effect.
As a prior art technique for making tone waveforms in electronic musical instruments, a waveform memory readout system is generally known in accordance with which tone actually generated acoustically from a natural musical instrument or the like is sampled and stored as waveform data in a memory or other suitable storage medium, and then the thus-stored waveform data are read out in accordance with phase angle data. This waveform memory readout system is advantageous in that it can provide tone of the same high quality as that provided by the corresponding natural musical instrument.
In such a waveform memory readout system, the waveform data are typically stored on just one cycle or plural cycles of a waveform. But, with a view to expressing time-varying changes in tone color etc., some type of the waveform memory readout system stores waveform data on the entire waveform, i.e., from beginning to end (from attack portion to decay portion) of the generated tone, so that they are thoroughly read out in response to a key depression on a keyboard.
Further, another type of the waveform memory readout system is also known in accordance with which, in order to easily make such data that require no large storage capacity, waveform data on the rise portion (attack portion) are stored for plural cycles and waveform data on the following sustain portion are stored for just one cycle, so that the plural-cycle waveform data are read out for reproducing the attack portion and then the one-cycle waveform data are read out for reproducing the sustain portion. With this type, the original tone can be stored in an effectively compressed state without lowering the tonal quality, and therefore it is possible to faithfully reproduce the original tone with high reality and abundant expression (Japanese Patent Laid-open Publication No. 59-109090).
As mentioned above conventional electronic musical instruments reproductively generate a tone by reading out memory-stored waveform data with a readout speed (phase angle) that corresponds to the pitch of a tone to be generated. As a method for imparting a special effect in connection with the waveform readout, some of the conventional electronic musical instruments control the waveform data readout speed by pitch bending, or time-varies the waveform data readout speed by using a pitch bend envelope generator to change the pitch bend depth (U.S. Pat. Nos. 4,179,971, 4,813,327 and 4,961,363).
However, the pitch bend control can only increase or decrease the pitch of generated tone and therefore can only time-varies the pitch of generated tone. Namely, with the prior art techniques, it is not at all possible to simulate such scratch effect sounds that can be provided by analog record reproduction devices (players), i.e., to simulate a sound effect that can be obtained by forcing a record to rotate in the reverse or reverse direction or to move irregularly.